1. Field of the Invention
The present invention relates to a lighting device. In particular, the present invention relates to a lighting device having a plane light-emitting body as a light source.
2. Description of the Related Art
In recent years, lighting devices provided with light sources utilizing organic electroluminescence (hereinafter also referred to as “organic EL” have been actively developed. The light sources are plane light-emitting bodies and have low directivity of emitted light. In general, the refractive index of a light-emitting region in the light source is higher than that of the air. Thus, total reflection of part of light emitted from the light source occurs at the interface with the air. As a result, the proportion of light emitted to the outside (in the air) of light emitted from the light source (hereinafter also referred to as light extraction efficiency) might be decreased, which is a problem.
A structure is disclosed in which a structure body is provided over a surface of a light source in order to solve such a problem. For example, Non-Patent Document 1 discloses a structure in which a high refractive index glass substrate and a high refractive index lens are used in combination and a structure in which a concave-convex structure is provided at the interface between a high refractive index glass substrate and the air. With the structure, light extraction efficiency can be improved.